As the lining structure of the lower vessel of the RH degasser, there has been known the structure described in patent document 1, for example. According to the description of the patent document 1, as shown in FIG. 7, there is disclosed the structure where a refractory 61 which constitutes a center block sandwiched between two circulating flow tubes 60 has the downwardly expanding reverse jack arch structure, and constitutes a part of tuyeres of the circulating flow tubes.
By adopting the above-mentioned structure, floating of the refractory 61 which constitutes the center block can be suppressed.
Further, in patent document 2, as shown in FIG. 6, the following structure is described. Ina lining of a bottom part of a vacuum vessel 50 provided with circulating flow holes 51 at two positions respectively, a row of lining bricks which are positioned between the circulating flow holes 51 are stacked in one direction in an inclined manner along a center line of the bottom part, a frontwardly tapered taper which extends toward an upper side of the circulating flow hole is formed on an upper outer peripheral surface 53 of a circulating flow tube brick 52, and side surfaces of a brick 54 which is positioned between the circulating flow holes 51 are widened upward with an angle which matches the taper of the upper peripheral surface of the circulating flow tube brick 52.